1. Field of the Invention
The present invention relates to an inerting method in which an oxygen content which is predefinable and reduced in comparison to normal ambient air is set and maintained in the spatial atmosphere of an enclosed room and in which the oxygen content in the enclosed room's spatial atmosphere can be quickly reduced further when the need arises.
The invention further relates to a corresponding system for reducing oxygen.
The inventive inerting method or the inventive inerting system respectively serves for example in minimizing risk and in extinguishing fires in a protected room subject to monitoring, whereby the enclosed room is continuously rendered inert to different lowered levels for the purpose of preventing or controlling fire.
2. Background Information
Among the examples of use for the inventive inerting method include providing hypoxic training conditions in an enclosed room in which the oxygen content has been reduced. Such a room enables training under artificially simulated high-altitude conditions, also referred to as “normobaric hypoxic training.” Another example of use is the storing of food, preferentially pomaceous fruit, in a controlled atmosphere (CA) in which the proportional percentage of atmospheric oxygen is regulated in order to, among other things, slow the aging process acting on the perishable merchandise.
The basic principle behind inerting technology to prevent fires is based on the knowledge that in enclosed rooms which are only entered occasionally by humans or animals, and in which the equipment housed therein reacts sensitively to the effects of water, the risk of fire can be countered by reducing the oxygen concentration in the relevant area to an average value of e.g. approximately 15% by volume. At such a (reduced) oxygen concentration, most combustible materials can no longer ignite. Accordingly, the main areas of application for inerting technology in preventing fires also include IT areas, electrical switching and distribution rooms, enclosed facilities as well as storage areas containing high-value commercial goods. The preventative effect resulting from this method is based on the principle of oxygen displacement. As is known, normal ambient air consists of 21% oxygen by volume, 78% nitrogen by volume and 1% by volume of other gases. For fire prevention purposes, the oxygen content of the spatial atmosphere within the enclosed room is decreased by introducing an oxygen-displacing gas, for example nitrogen. A preventative effect is known to begin as soon as the percentage of oxygen drops below about 15% by volume. Depending upon the flammable substances stored in the protected room, it may be necessary to further lower the percentage of oxygen to, for example, 12% by volume.
This type of inerting system is known in principle in the prior art. For example, the published DE 198 11 851 A1 document describes an inerting system designed to lower the oxygen content in an enclosed room (hereinafter also referred to as “protected room”) to a specific base inerting level and, in the event of a fire, to quickly lower the oxygen content further to a specific full inerting level.
The term “base inerting level” as used herein is to be understood as referring to a reduced oxygen content compared to the oxygen content of the normal ambient air, however whereby this reduced oxygen content poses no danger of any kind to persons or animals such that they can still enter into the protected room without any problem (i.e. without any special protective measures such as oxygen masks, for example). The base inerting level corresponds to an oxygen content within the protected room of e.g. approximately 15% to 17% by volume.
On the other hand, the term “full inerting level” is to be understood as referring to an oxygen content which has been further reduced compared to the oxygen content of the base inerting level such that the flammability of most materials has already been decreased to a level at which that they are no longer able to ignite. Depending upon the fire load inside the respective protected room, the full inerting level generally ranges from 12% to 14% of oxygen concentration by volume.
In the multi-stage inerting method known from the DE 198 11 851 A1 printed publication, in which the oxygen content is progressively lowered, an inerting technology for preventing fires is thus employed with which the oxygen content in the protected room is first reduced to a specific lowered level (base inerting level) of e.g. 17% by volume, whereby in the event of a fire or when otherwise needed, the oxygen content is then further reduced to a specific full inerting level of e.g. 13.8% by volume or less. If an inert gas generator, for example a nitrogen generator, is used as the inert gas source in such a two-stage inerting method for reducing the oxygen content to the first lowered level (base inerting level), the number of high-pressure gas tanks needed for full inertization, in which the oxygen-displacing gas or gas mixture (hereinafter also referred to simply as “inert gas”) is stored in compressed form, can be kept low.
However, relatively high capital investments are required in order to realize the above-described and known per se two-stage inerting method since the two-stage inerting method places specific demands on the inert gas sources needed to supply the inert gas. Specifically, conventional two-stage inerting systems provide without exception for two separate inert gas sources since a distinction must be made when setting a specific inerting level (lowered level) as to whether a base inerting level or a full inerting level is to be set in the atmosphere of the room. It hereby needs to be considered that—starting from a previously set base inerting level—the lowering to a full inerting level needs to occur according to a predefined sequence of events and particularly within a predefined period of time after an alarm has been issued. In contrast, it is not necessary for the base inerting level to be set according to a predefined inerting curve.
To be understood by the term “inerting curve” as used herein is the temporal gradient of the oxygen content when oxygen-displacing gas (inert gas) is introduced into the spatial atmosphere of the protected room.
Because a distinction must be made when setting a specific inerting level as to whether a base inerting level or a full inerting level is to be set in the atmosphere of the room, the inert gas sources needed to supply the corresponding inert gas for setting the base/full inerting level are subject to different requirements. In the case of lowering to the full inerting level, the inert gas sources employed must allow for being able to provide an accordingly large enough amount of inert gas per unit of time so as to be able to set the full inerting level in the protected room's spatial atmosphere within the predefined period of time. Accordingly, the inert gas source employed for lowering to the full inerting level must have the appropriate capacity.
The inert gas source is however not subject to this requirement if only the base inerting level is to be set. As explained above, it is hereby normally not necessary to follow a predefined inerting curve and particularly adhere to a predefined period of time when lowering to the base inerting level. Accordingly, the inert gas source used to lower to a base inerting level can be of correspondingly smaller dimensions in terms of its output capacity.
For these reasons, in practical application of the two-stage inerting method, two separate inert gas sources are usually used: a nitrogen generator only able to supply a relatively small amount of inert gas (here: nitrogen-enriched air) per unit of time and used to set and maintain a base inerting level; and a high-pressure gas storage tank in which an oxygen-displacing gas or gas mixture is stored in compressed form for the purpose of being able to quickly set a full inerting level in the spatial atmosphere of the enclosed room when needed.
The use of two separate inert gas sources to realize the two-stage inerting method is coupled with the disadvantage of relatively high initial capital costs. In addition, the space that needs to be provided for storing the two separate insert gas sources (nitrogen generator on the one hand and high-pressure gas storage tank on the other) cannot be realized in some applications without undertaking major structural measures.